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Lactose Intolerance Symptoms

John Bankston John Bankston April 23, 2021
Medically reviewed by Susan Kerrigan, MD and Marianne Madsen

Mammals usually stop drinking milk after infancy. Humans are different; we don’t just consume dairy products as adults, but we drink milk from other species, too. Not everyone can drink milk indiscriminately. In fact, around two-thirds of the world’s adults have lactose intolerance symptoms. So what are the signs of lactose intolerance? What are the best ways to manage it? Are some dairy products more triggering than others? The first step is understanding the condition. 


Mother’s Milk


When you think about it, a cow is nature’s refrigerator. After consuming grasses humans can’t eat, they transform their veggies into milk. Dairy products are loaded with nutrition and essentially available whenever a farmer desires. So it’s not surprising that our ability to tolerate lactose traces back to when humans shifted from hunting and gathering to farming. Lactose tolerance isn’t a common trait. Its expression is linked to colder climates–places where milk left out in the morning will still be chilled (and drinkable) in the afternoon. The mutation near the gene which produces the lactase enzyme probably began 8,000 years ago in the region where Turkey is today. This is when farmers began milking those recently domesticated sheep, goats, and, of course, cows. In other parts of the world, the mutation wasn’t as likely to be passed on. In Europe, being able to drink milk may have saved people from starvation during periods when crops like barley or wheat weren’t growing.


Lactase is produced in the small intestines of most humans. This enzyme allows our bodies to process the sugar unique to dairy products––lactose. Lactase transforms milk sugar into glucose and galactose. This pair of simple sugars then travels through the intestinal lining and into our bloodstream. When someone with a low level of lactase consumes a dairy product, the lactose is not absorbed. Instead it heads right to the colon where it is attacked by bacteria. This process initiates the bloating and other common symptoms of lactose intolerance


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Lactose Intolerance

Lactose Intolerance

One reason the enzyme’s ability to do its job declines is that tweens and teens often drink less milk than they did as children. The enzyme essentially atrophies like an unused muscle. This leads to the most common type of lactose intolerance: primary lactose intolerance. This is usually seen in adults because of a sharp reduction in the production of lactase. It is more common for people with ancestors from Africa or Asia than for those who trace their families to Europe. In the United States, Native Americans are also more likely to have the condition.


A less common form occurs when the small intestine recovers from surgery or illness. This secondary lactose intolerance is seen in people with Crohn’s disease or celiac disease along with those who have suffered an intestinal infection or other malady. Often treating the condition allows the patient to slowly reintroduce dairy products into their diet. 


Perhaps the most challenging form of lactose intolerance is congenital or developmental lactose intolerance. This is because infants usually get their nutrition exclusively from milk. Fortunately, this is a rare disorder, and both parents have to have the same gene variant in order for it to be expressed in their child. Those born prematurely are also more likely to be lactose intolerant. This is because lactase enzyme levels increase in utero and often don’t fully develop until the ninth month of pregnancy. In both cases, lactose-free formula is recommended if breastfeeding is not possible.


Determining whether or not you are lactose intolerant is an important step. Feeling bloated the day after consuming the contents of a large cheese plate is not necessarily a sign of lactose intolerance. Symptoms of lactose intolerance usually manifest between thirty minutes to two hours after consuming a dairy product. These include bloating, nausea, and diarrhea.


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Foods to Avoid For Diarrhea

Foods to Avoid For Diarrhea

Avoiding milk and other dairy products is not ideal. Studies show that these products have numerous health benefits for all age groups, including reducing the risk of obesity or high blood pressure along with improving bone and tooth health. Even chocolate milk has been used effectively as a recovery aid after prolonged endurance exercises. It was actually superior to several sports drinks! Nonfat or skim milk offers a high-protein, vitamin-filled beverage with none of the fat of whole milk. 


If you have lactose intolerance symptoms, keep in mind that you may still be able to enjoy one half cup of milk at one sitting–around two to four ounces or  60 to 120 milliliters. Other dairy products that may be less problematic include buttermilk, goat’s milk, and aged hard cheese. Despite being lactose intolerant, many of our ancestors consumed cheese. Remember, if you have any of the signs of lactose intolerance and are avoiding dairy products because of it, you need to find ways to replace them nutritionally including taking supplements or eating more green, leafy vegetables. 

Doctor Profile

John Bankston


John Bankston is a published author of over 150 nonfiction books for children and young adults including biographies of Jonas Salk, Gerhard Domak, and Frederick Banting.

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